Transmission of nerve impulses

This is in continuation to the last article focusing on neural system and mechanisms of neural coordination in a human body.

Hyderabad: This is in continuation to the last article focusing on neural system and mechanisms of neural coordination in a human body. In today’s article we continue to learn more about how nerve impulses are generated, conducted and transmitted.

Generation and conduction of nerve impulse

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In the last article, we discussed learnt that the electrical potential difference across the plasma membrane at the site A is called the action potential, which is, in fact, termed as a nerve impulse.

• At sites immediately ahead, the axon (e.g., site B) membrane has a positive charge on the outer surface and a negative charge on its inner surface.

• As a result, a current flows on the inner surface from site A to site B.

• On the outer surface, current flows from site B to site A to complete the circuit of the current flow.

• Hence, the polarity at the site is reversed, and an action potential is generated at site B.

• Thus, the impulse (action potential) generated at site A arrives at site B.

• The sequence is repeated along the length of the axon and consequently the impulse is conducted.

• The rise in the stimulus-induced permeability to Na is extremely short-lived. It is quickly followed by a rise in permeability to K .

• Within a fraction of a second, K diffuses outside the membrane and restores the resting potential of the membrane at the site of excitation and the fibre becomes once more responsive to further stimulation.

Transmission of impulses

• A nerve impulse is transmitted from one neuron to another through junctions called synapses.

• A synapse is formed by the membranes of a pre-synaptic neuron and a post-synaptic neuron, which may or may not be separated by a gap called synaptic cleft.

• There are two types of synapses, namely, electrical synapses and chemical synapses.

• At electrical synapses, the membranes of pre- and post-synaptic neurons are in very close proximity.

• Electrical current can flow directly from one neuron into the other across these synapses.

• Transmission of an impulse across electrical synapses is very similar to impulse conduction along a single axon.

• Impulse transmission across an electrical synapse is always faster than that across a chemical synapse.
• Electrical synapses are rare in our system.
• At a chemical synapse, the membranes of the pre- and post-synaptic neurons are separated by a fluid-filled space called synaptic clef.
• Chemicals called neurotransmitters are involved in the transmission of impulses at these synapses.
• The axon terminals contain vesicles filled with these neurotransmitters.
To be continued…

By
Dr. Modala Mallesh
Subject Expert

Palem, Nakrekal, Nalgonda

9989535675